VARI as an indicator of site productivity of Pinus taeda L.: soil, litter, and plant nutrition

Authors: ERCOLE, TAMIRES - Universidade Tuiti Do Parana; GOMES, JOÃO BOSCO - Brazilian Agricultural Research Corporation (EMBRAPA); RODRIGUES, VALDÉCIO - Universidade Tuiti Do Parana; TRENTIN, NICOLAS - Universidade Tuiti Do Parana; DE OLIVEIRA JUNIOR, JAIRO - Universidade Tuiti Do Parana; ASSIS-PEREIRA, GABRIEL - Universidad De Sao Paulo; FILHO, MARIO - Universidad De Sao Paulo; MOURA, AMANDA - Non ARS Employee; MAEDA, SHIZUO - Brazilian Agricultural Research Corporation (EMBRAPA); Prior, Stephen - Steve; CONSALTER, RANGEL - Non ARS Employee; MOTTA, ANTÔNIO - Universidade Tuiti Do Parana

Submitted to: European Journal of Forest Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2024
Publication Date: 6/27/2024
Citation: Ercole, T.M., Gomes, J.B.V., Rodrigues, V.S., Trentin, N.S., Junior, J.C.O., Pereira, G.A., Filho, M.T., Moura, A.P.C., Maeda, S., Prior, S.A., Consalter, R., and Motta, A.C.V. 2024. VARI as an indicator of site productivity of Pinus taeda L.: soil, litter, and plant nutrition. European Journal of Forest Research. https://doi.org/10.1007/s10342-024-01711-y.
DOI: https://doi.org/10.1007/s10342-024-01711-y

Interpretive Summary: Pinus taeda L. forests can show great growth variation in southern Brazil. This study used drone technology to verify if Visible Atmospherically Resistant Index (VARI) could captured tree growth heterogeneity. Areas classified as Very Low VARI had smaller tree growth and symptoms of needle chlorosis similar to reports of Mg deficiency. Needle Mg was well below values considered to be critical (0.8 g kg-1), and our findings suggest reestablishing the critical level as 0.3 g kg-1. Low Mg in fine roots and tree bark supported needle observations. Similar findings were noted for litter, with these areas having high litter amounts. In addition, high values of Al along with low Mg in soil could favor Mg deficiency in trees. Overall, low nutrients levels in soil parent material, intense leaching, and soil depletion by nutrient export (harvests) are critical factors causing Mg deficiency as confirmed by chlorotic symptoms and low Mg concentrations in tree tissue. Another possible factor influencing Mg deficiency was low concentrations of Ca in soil, tree tissues, and litter.

Technical Abstract: In commercial Pinus taeda stands, the appearance of needle chlorosis has intensified in low growth areas. Goals of this study were to verify if Visible Atmospherically Resistant Index (VARI) captures heterogeneity of Pinus taeda development and to determine what specific factors are associated with occurrence of chlorotic symptoms. We evaluated a 14 year-old reforested P. taeda stand that had already undergone two thinnings; the study area encompassed 18.42 ha on soil derived from acidic igneous parent material. A VARI map was used to delineate the area into four classes: Very Low, Low, Medium, and High. In each class, tree growth was evaluated, and samples of tree tissue (needles, trunk cross sections, and fine roots), litter, and soil were collected for evaluation. There were no differences in soil classification and fertility between classes for this acidic low fertility soil. Compared to the lower VARI classes (Low and Very Low), tree wood volume (without bark) of the High class was 0.20 m³ higher. Higher VARI classes showed greater concentrations of Ca and Mg in needles, bark, and fine roots. The High class also showed higher concentrations of Ca and Mg in litter, but with less litter accumulation. Chlorosis symptoms (yellowing) at needle tips and tree crown loss in the Very Low VARI class were indicative of Mg deficiency, which likely caused reduced tree development.